What this is
ScrewBoltChart is a free, browser-based engineering reference for fasteners. It does two jobs. First, it turns your screen into a calibrated 1:1 measuring surface: lay a screw, bolt, nut or drill bit on the glass and read its size off true-scale jaws, combs and V-gauges. Second, it answers the questions that follow: the tap drill, the clearance hole, the wrench, the hex key, the thread pitch and a starting torque.
Everything runs in your browser. There are no accounts, no uploads and no server-side processing of anything you measure.
How 1:1 works
Browsers report CSS pixels, not millimetres, and every screen packs them differently. ScrewBoltChart asks you to calibrate once: match an on-screen outline to a coin or a standard ID-1 card (85.60 × 53.98 mm), or pick your device from the preset list. From that it knows how many pixels make a millimetre on your display and draws every gauge at true size.
- A card calibration is good to roughly ±0.25%; a coin to roughly ±0.8%.
- Browser zoom and pinch-zoom break the scale, so the header shows a warning when they change.
- The printable gauges need no calibration at all, because SVG millimetres print true at 100% scale.
Where the numbers come from
The dimensional data is generated from the governing standards by a build script and checked by a separate verification script before every release. Values are never typed by hand into the tables. Sources include:
- Threads: ASME B1.1 (Unified inch), ISO 261 and ISO 262 (metric), ASME B1.20.1 (NPT and NPSM pipe), ISO 7-1 and ISO 228-1 (BSP).
- Heads and keys: ASME B18.2.1, ASME B18.3, ASME B18.6.1, ISO 4762, ISO 4017, ISO 7380, ISO 10642, ISO 4026.
- Nuts, washers and clearance: ISO 4032, DIN 934, ASME B18.22.1, ISO 7089, ISO 273.
- Strength and torque: SAE J429 and ISO 898-1 proof loads, with a stated nut factor.
Where a figure is a shop convention rather than a standard value, such as a hardware-store drill substitute or a wood-screw pilot hole, the page says so.
What it is not
An on-screen gauge is a fast way to identify a part, not an inspection instrument. It will reliably tell a #8 from a #10, or M5 from M6, and it will tell you which pitch comb seats. It will not replace a micrometer, a thread ring gauge or a certified torque procedure. For anything safety-critical, confirm against the standard and the manufacturer's data.
Who runs it
ScrewBoltChart is an independent reference published under the ScrewBoltChart Engineering Reference name. Found a number that disagrees with your standard? Write to contact@screwboltchart.com or use the contact page, and include the source so the correction can be checked and fixed at the generator.